AQI Scale Explained
PM2.5 Levels & Health Effects
The Air Quality Index (AQI) measures air pollution on a scale of 0 to 500. Higher values mean more pollution and greater health risk.
AQI Levels at a Glance
Good (AQI 0–50)
PM2.5: 0–12.0 µg/m³
Health Effects: Air quality is satisfactory. Air pollution poses little or no risk.
What to Do: Enjoy outdoor activities freely. No precautions needed.
Moderate (AQI 51–100)
PM2.5: 12.1–35.4 µg/m³
Health Effects: Air quality is acceptable. However, unusually sensitive people may experience minor respiratory symptoms.
What to Do: Most people can continue outdoor activities normally. Sensitive individuals should monitor symptoms.
Unhealthy for Sensitive Groups (AQI 101–150)
PM2.5: 35.5–55.4 µg/m³
Health Effects: Members of sensitive groups (children, elderly, people with respiratory or heart conditions) may experience health effects. The general public is less likely to be affected.
What to Do: Sensitive groups should limit prolonged outdoor exertion. Consider moving activities indoors.
Unhealthy (AQI 151–200)
PM2.5: 55.5–150.4 µg/m³
Health Effects: Everyone may begin to experience health effects. Sensitive groups may experience more serious effects.
What to Do: Everyone should reduce prolonged outdoor exertion. Consider wearing an N95 mask outdoors. Use air purifiers indoors.
Very Unhealthy (AQI 201–300)
PM2.5: 150.5–250.4 µg/m³
Health Effects: Health alert: everyone may experience more serious health effects including respiratory irritation and aggravation of heart or lung disease.
What to Do: Avoid all outdoor physical activities. Keep windows closed. Use N95 masks if you must go outside. Run air purifiers continuously.
Hazardous (AQI 301–500)
PM2.5: 250.5+ µg/m³
Health Effects: Health warning of emergency conditions. The entire population is at risk of serious health effects.
What to Do: Stay indoors with air purification. Avoid all outdoor activities. Seal windows and doors. Seek medical attention if experiencing symptoms.
What is PM2.5?
PM2.5 stands for Particulate Matter with a diameter of 2.5 micrometers or less — about 30 times smaller than a human hair. These microscopic particles are produced by vehicle exhaust, industrial emissions, wildfires, and other combustion sources.
PM2.5 is considered the most dangerous common air pollutant because it can penetrate deep into the lungs and even enter the bloodstream. Long-term exposure is linked to respiratory disease, heart disease, stroke, and lung cancer. The World Health Organization recommends annual average PM2.5 levels below 15 µg/m³ and 24-hour averages below 45 µg/m³.
Frequently Asked Questions
What is a good AQI level?
An AQI of 0–50 is considered "Good." Air quality is satisfactory and air pollution poses little or no risk. You can enjoy outdoor activities without any health concerns.
At what AQI should I wear a mask?
You should consider wearing an N95 mask when AQI exceeds 150 (Unhealthy). At AQI 101–150, sensitive groups should take precautions. Above 200, everyone should wear masks outdoors.
What is PM2.5 and why is it dangerous?
PM2.5 refers to fine particulate matter smaller than 2.5 micrometers. These particles are dangerous because they can penetrate deep into the lungs and enter the bloodstream, causing respiratory and cardiovascular problems. The WHO recommends annual PM2.5 levels below 15 µg/m³.
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